The invention relates to program patching methods, and in particular to program patching methods and systems using bus address translation.
A microprocessor system generally contains a read-only-memory (ROM) to store programs or firmware. The programs or firmware can be retrieved and executed by a microprocessor through address buses. An electronic product, such as a DVD player, or a computer, may contain a microprocessor system with a ROM for system controlling.
A ROM in a microprocessor system is generally called an on-chip ROM. While a ROM is a non-writable device, the ROM in a microprocessor system generally stores permanent data. When an electronic product with an on-chip ROM is delivered to a customer, the data stored in the ROM is unchangeable.
If a program in a ROM contains erroneous code or requires modification, a program patch may be executed for such correction or modification. U.S. Pat. No. 4,542,453 discloses a data processing system, using one bit for each potential ROM address to indicate a program branch for programs in a ROM. U.S. Pat. No. 5,581,776 provides a branch control system for ROM-programmed processors, which modifies a program counter for manifesting program count values and executing a prestored program in accordance with the program count values. Additionally, U.S. Pat. No. 6,237,120 discloses a method of program patching a ROM, which changes the address of a microprocessor by hardware interrupt to execute the program patch.
The mentioned methods and systems have some drawbacks. For example, using one bit for each potential ROM address may heavily increase system load. Modifying a program counter for a branch lacks flexibility as it can only branch for one source/target pair. Changing microprocessor addresses cannot be applied to certain systems, such as a system with pipelined CPU (central processing unit). Therefore, a more flexible and low cost method and system is desirable.